Circles are an important part of geometry, with applications in a variety of fields.

Farmers use irrigation systems that water fields in a circle, generating circular crop areas, such as these shown in eastern Oregon.

Engineers use the geometry of circles to construct bridges, such as the Mike O'Callaghanâ€“Pat Tillman Memorial Bridge that crosses the Colorado River between Nevada and Arizona near Hoover Dam.

Park designers use circles to design fountains such as Mecom Fountain in Hermann Park near downtown Houston, Texas.

Because circles are so commonly used, it is important to be able to use geometric ideas and concepts to describe them. In this lesson, you will extend what you know about area to develop and apply ways to calculate the area of a sector of a circle, which is a pie-shaded wedge of a circle created by a central angle between two radii.